This invention relates generally to a switch which is responsive to an ambient temperature level.
The invention more particularly relates to an unresettable switch which will open a circuit when the ambient temperature around the circuit is increased to a predetermined level.
Switches of the type described have become necessary to protect various circuitry in devices such as appliances, etc., from the hazards of high temperatures generated therein. An increasing awareness of the hazards that present themselves as a result of a device which is capable of generating unchecked levels of heat emphasizes the importance of incorporating thermal switches in such devices. Not only destruction to the device but to the immediate surroundings could possibly be eliminated through the use of a switch which is capable of accurately sensing the increase in ambient temperature level to a predetermined amount and quickly and reliably opening the circuit to stop the flow of current therein.
Prior art devices of the type described are generally multipiece units with a conductive casing. The multipiece devices of the prior art are inherently costly to produce with a high level of quality control. One such prior art device utilizes a pair of coaxially arranged conductor wires, one of which is electrically connected to an outer conductive casing and the second of which is placed in releasable contact with the conductive casing through a thin washer member. The washer member is urged into contact with the second conductor wire through a spring and a thermal pellet. When a predetermined temperature level is reached, the thermal pellet liquifies, thus releasing the spring energy and allowing a secondary spring to force the washer out of contact with the second conductor wire. Such a device has approximately eight to ten different elements not including the conductor wires.
It is the primary object of the invention to provide a thermal switch device with a minimum of elements.
A further object of the invention is to provide a thermal switch device which is capable of quickly and reliably opening a circuit at a predetermined temperature level.
A still further object of the invention is to provide a thermal switch device which distributes spring loading energy over a relatively large surface area of heat fusible material.
Still a further object of the invention is to provide a thermal switch device which provides a lever arm construction to maximize the contact force while minimizing the unit reaction force on heat fusible encapsulating material.
The above and other objects and advantages are achieved by the present invention which basically provides for the encapsulation of contact regions of conductor wires, when spring loaded into contact with each other, with a heat fusible material, such as an appropriate organic mixture, followed by a coating or encapsulation of a rigid insulating material providing a structural and protective encasement for the circuitry while insulating the conductor wires from one another except at the contact region. Spring energy is provided in the system by forcing a section of at least one of the conductor wires inwardly against a bias. A localized contact region is provided below the spring bias region so that contact regions maybe forced together into electrical contact by a lateral compression force and dipped or encapsulated in a heat fusible material. The contact region is spaced upwardly from the terminal extremities of the conductor wires which are initially interconnected so that the contract regions serve as a fulcrum with stored energy distributed over a relatively large surface of heat fusible material by a lever arm. The terminal extremities are severed after the energy has been stored and the exposed extremities are coated with heat fusible material. The heat fusible material will be encapsulated with a rigid insulating material to structurally support the circuit. The encapsulated region will thus provide a closed circuit until the fusible material flows releasing the energy stored in the spring.